Nonaqueous electrolyte secondary battery and battery
module

ABSTRACT

A nonaqueous electrolyte secondary battery, having an internal resistance of 10 mΩ or less as an alternating-current impedance value of 1 kHz, comprises a metal outer container, a nonaqueous electrolyte contained in the container, a positive electrode contained in the container, a negative electrode contained in the container, a separator interposed between the negative electrode and the positive electrode, a negative electrode lead having one end connected to the negative electrode, and a negative electrode terminal attached to the outer container so as to be connected electrically to the other end of the negative electrode lead, at least the surface of the negative electrode terminal which is connected to the negative electrode lead being formed of aluminum alloy with an aluminum purity of less than 99 wt. % containing at least one metal selected from the group consisting of Mg, Cr, Mn, Cu, Si, Fe and Ni.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.14/157,614, filed Jan. 17, 2014, now allowed; which is a division ofU.S. patent application Ser. No. 13/898,529, filed May 21, 2013, nowU.S. Pat. No. 8,669,006; which, in turn, is a division of U.S. patentapplication Ser. No. 13/567,143, filed Aug. 6, 2012, now U.S. Pat. No.8,470,474; which, in turn, is a division of U.S. patent application Ser.No. 13/231,056, filed Sep. 13, 2011, now U.S. Pat. No. 8,268,482, which,in turn, is a division of U.S. patent application Ser. No. 12/981,756,filed Dec. 30, 2010, now U.S. Pat. No. 8,043,739, which, in turn, is acontinuation of U.S. patent application Ser. No. 11/470,482, now U.S.Pat. No. 7,892,674, filed Sep. 6, 2006, the disclosures of which areincorporated herein by reference in their entireties. This applicationclaims the benefit of priority from prior Japanese Patent ApplicationNo. 2005-262580, filed Sep. 9, 2005, the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a nonaqueous electrolyte secondary battery anda battery module.

2. Description of the Related Art

A nonaqueous electrolyte secondary battery using a lithium metal,lithium alloy, lithium compound or carbon material for its negativeelectrode is expected as a high energy density battery or high outputdensity battery, and it has been intensively researched and developed.So far, lithium batteries comprising a positive electrode containingLiCoO₂ or LiMn₂O₄ as an active material and a negative electrodecontaining a carbon material for intercalating and deintercalatinglithium ions have been widely put in practical use. In the negativeelectrode, various materials which are a substitute for the carbonmaterial are being studied, such as metal oxides and alloys.

In a nonaqueous electrolyte secondary battery, a copper foil isgenerally used as a current collector of a negative electrode. A leadand a terminal to which the lead is connected are usually made of copperor nickel. A secondary battery comprising a negative electrode includinga current collector of copper foil is elevated in potential of thenegative electrode in an overdischarged state. Accordingly, thedissolving reaction of the negative electrode made of copper foil ispromoted, and the discharge capacity drops suddenly. When a long cyclecontinues in a battery module, a battery capacity balance is broken, andoverdischarge may occur in certain batteries. For this reason, thecurrent collector made of copper foil, which is assembled in a batteryin an overdischarged state begins to dissolve. Therefore, the secondarybattery is provided with a protective circuit for preventing itself frombeing overdischarged.

However, since such a protective circuit is installed, the secondarybattery is reduced in energy density. If an outer container having athin metal can is used in order to reduce the battery weight, copper forcomposing the current collector of the negative electrode, lead andterminal is dissolved, for example, at the time of overdischarging, andswelling of the battery increases.

Hence, JP-A. 2004-296256 (KOKAI) discloses a nonaqueous electrolytesecondary battery using an aluminum foil or aluminum alloy foil for anegative electrode current collector, in use of a negative electrodeactive material for intercalating lithium ions at a specific potential.Such a configuration makes it possible to realize a nonaqueouselectrolyte secondary battery enhanced in energy density andoverdischarge cycle performance. Further, since this nonaqueouselectrolyte secondary battery can elevate the discharge capacity overseveral Ah or tens Ah, it is highly expected to be used as a squarenonaqueous electrolyte secondary battery for use in, aside from electricpower storage, vehicles such as a power-assisted bicycle, electricscooter, electric vehicle, hybrid vehicle, and electric train.

An on-board secondary battery is required to be low in internalresistance, high in energy density, and high in output density, for thepurpose of obtaining high output. Further, excellent cycle performance,and high strength and corrosion resistance of materials for a longperiod are demanded in the conditions of high temperature, highhumidity, vibration, quick charging, high output discharge, andoverdischarge. Therefore, for the purpose of maintaining the internalresistance of the battery at a low level, a connecting portion between alead and a terminal where current in the battery is concentrated isrequired to be high in mechanical strength, electrochemical stability,and chemical stability in the high temperature and high humidityenvironment for a long period, thereby maintaining low resistanceexcellent in corrosion resistance.

However, when in the secondary battery described above, the lead andterminal of the negative electrode are formed of copper with anexcellent conductivity, a corrosion or dissolving reaction may beadvanced in the connecting portion between the lead and terminal in anoverdischarge operation of the battery or high temperature and highhumidity environment over a long period of use, and thereby theresistance is increased. For this reason, it becomes difficult to obtainhigh output from the battery and battery module. Further, since theimpedance is increased, the discharge reaction of the positive electrodeand negative electrode is not promoted sufficiently in high outputdischarge, and a utility rate of an active material is lowered.

On the other hand, JP-A 2003-36825(KOKAI) discloses a nonaqueouselectrolyte battery high in safety, the battery having a terminalstructure capable of preventing or suppressing sparks possibly occurringin a terminal unit due to leak of a nonaqueous electrolyte. Thisdocument, in paragraph[0036], discloses that a negative electrodeterminal 40 made of copper alloy is composed of a current collector 40 aserving as an internal terminal and a bolt-like external terminal unit40 b; that the current collector 40 a is bonded to a band-like negativeelectrode lead 12 a extending from an electrode body 10; that theexternal terminal unit 40 b is positioned outside of a negativeelectrode side lid plate 23 of a battery case 20; and that the exposedsurface portion is plated with aluminum to prevent spark generation.

In the nonaqueous electrolyte battery, the current collector 40 a of thenegative electrode terminal 40 to which the negative electrode lead isconnected is made of copper alloy. Therefore, as mentioned above, acorrosion or dissolving reaction is promoted in a connecting portionbetween the lead and terminal in an overdischarge operation of thebattery or high temperature and high humidity environment over a longperiod of use, and the internal resistance increases. Consequently, itbecomes difficult to obtain a high output from the battery or batterymodule.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda nonaqueous electrolyte secondary battery having an internal resistanceof 10 mΩ or less at an alternating-current impedance value of 1 kHz,comprising;

a metal outer container;

a nonaqueous electrolyte contained in the container;

a positive electrode contained in the container;

a negative electrode contained in the container and having an activematerial for intercalating lithium ions at a potential of 0.4 V or morewith respect to an electrode potential of lithium;

a separator interposed between the negative electrode and the positiveelectrode;

a negative electrode lead having one end connected to the negativeelectrode, the negative electrode lead being made of aluminum with apurity of 99 wt. % or more, or aluminum alloy with an aluminum purity of99 wt. % or more; and

a negative electrode terminal attached to the outer container so as tobe connected electrically to the other end of the negative electrodelead, at least the surface of the negative electrode terminal which isconnected to the negative electrode lead being formed of aluminum alloywith an aluminum purity of less than 99 wt. % containing at least onemetal selected from the group consisting of Mg, Cr, Mn, Cu, Si, Fe andNi.

According to a second aspect of the present invention, there is provideda battery module assembled by connecting a plurality of nonaqueouselectrolyte secondary batteries recited in the first aspect.

According to a third aspect of the present invention, there is provideda nonaqueous electrolyte secondary battery having an internal resistanceof 10 mΩ or less at an alternating-current impedance value of 1 kHz,comprising;

a metal outer container serving also as a negative electrode terminal;

a nonaqueous electrolyte contained in the container;

a positive electrode contained in the container;

a negative electrode contained in the container and having an activematerial for intercalating lithium ions at a potential of 0.4 V or morewith respect to an electrode potential of lithium;

a separator interposed between the negative electrode and the positiveelectrode; and

a negative electrode lead having one end connected to the negativeelectrode, and the other end connected to the inner side of thecontainer, the negative electrode lead being made of aluminum with apurity of 99 wt. % or more, or aluminum alloy with an aluminum purity of99 wt. % or more,

wherein at least the inner surface of the outer container which isconnected to the negative electrode lead is formed of aluminum alloywith an aluminum purity of less than 99 wt. % containing at least onemetal selected from the group consisting of Mg, Cr, Mn, Cu, Si, Fe andNi.

According to a fourth aspect of the present invention, there is provideda battery module assembled by connecting a plurality of nonaqueouselectrolyte secondary batteries recited in the third aspect.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a sectional view showing a square nonaqueous electrolytesecondary battery according to a first embodiment;

FIG. 2 is a sectional view across a negative electrode terminal of thesecondary battery in FIG. 1;

FIG. 3 is a perspective view showing a laminated electrode groupcontained in an outer container in FIG. 1;

FIG. 4 is a sectional view showing another configuration of the negativeelectrode for use in the square nonaqueous electrolyte secondary batteryaccording to the first embodiment;

FIG. 5 is a sectional view of a further another configuration of thenegative electrode for use in the square nonaqueous electrolytesecondary battery according to the first embodiment;

FIG. 6 is a perspective view showing a battery module according to thefirst embodiment;

FIG. 7 is a sectional view showing a square nonaqueous electrolytesecondary battery according to a second embodiment;

FIG. 8 is a sectional view across a negative electrode lead of thesecondary battery in FIG. 7; and

FIG. 9 is a perspective view showing a battery module according to thesecond embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention mainly refer to a square nonaqueouselectrolyte secondary battery and battery module, but circularnonaqueous electrolyte secondary batteries and the like are alsoincluded in the scope of the present invention.

First Embodiment

A square nonaqueous electrolyte secondary battery according to a firstembodiment comprises a metal outer container, a nonaqueous electrolytecontained in the container, a positive electrode contained in thecontainer, a negative electrode contained in the container and having anactive material for intercalating lithium ions at a potential of 0.4 Vor more with respect to an electrode potential of lithium, and aseparator interposed between the negative electrode and the positiveelectrode. A negative electrode lead has one end connected to thenegative electrode. The negative electrode lead is made of aluminum witha purity of 99 wt. % or more, or aluminum alloy with an aluminum purityof 99 wt. % or more. A negative electrode terminal is attached to thecontainer so as to be connected to the other end of the negativeelectrode lead. At least the surface of the negative electrode terminalconnected to the negative electrode lead is formed of aluminum alloywith aluminum purity of less than 99 wt. % containing at least one metalselected from the group consisting of Mg, Cr, Mn, Cu, Si, Fe and Ni. Thepositive electrode is connected to a positive electrode terminalattached, for example, to the container through a lead. Such a secondarybattery has an internal resistance of about 10 mΩ or less as analternating-current impedance value of 1 kHz. More specifically, thesecondary battery has a large discharge capacity of, for example, 2 Ahor more.

The negative electrode, positive electrode, separator, nonaqueouselectrolyte, and outer container will be specifically described below.

1) Negative Electrode

The negative electrode includes a current collector, and a negativeelectrode layer held on one side or both sides of the current collectorand having an active material, a conductive agent, and a binder.

The current collector is made of, for example, aluminum foil or aluminumalloy foil with a purity of 99 wt. % or more. The aluminum alloy ispreferably an alloy containing a metal such as Mg, Zn, Mn, or Si. Asidefrom the metal, the aluminum alloy preferably contains transition metalsuch as Fe, Cu, Ni, or Cr at 100 ppm or less.

The aluminum foil or aluminum alloy foil use as the current collector ispreferably 50 μm or less in average diameter of crystal grains. A morepreferred average diameter of crystal grains is 10 μm or less. Here, anaverage diameter d of crystal grains of aluminum and aluminum alloyrepresents the average diameter of the particles. The texture of anobject material surface is observed by a metal microscope, the number ofcrystal grains n existing in an area of 1 mm×1 mm is counted, and Anaverage area S of crystal grains is calculated from the formulaS=(1×10⁶)/n (μm²). At five positions in the metal microscopeobservation, crystal grains are counted, the average area of the crystalgrains is used in the following formula (1), and the average iscalculated, so that the average diameter d (μm) of crystal grains isdetermined. An assumed error is about 5 wt. %.

d=2(S/π)^(1/2)  (1)

The size of the crystal grains of aluminum foil or aluminum alloy foilvaries widely depending on many factors, including a materialcomposition, impurities, processing condition, heat treatment history,annealing condition and cooling condition. By properly combining andadjusting the factors in a manufacturing process, aluminum foil oraluminum alloy foil having an average diameter of crystal grains of 50μm or less can be manufactured. The current collector may bemanufactured from PACAL21 (registered trademark) manufactured by NipponFoil Mfg. Co., Ltd.

Such an aluminum foil or aluminum alloy foil having an average diameterof crystal grains of 50 μm or less can increase the strengthdramatically. An increase of the strength of the current collectorimproves the physical and chemical tolerance, therefore the currentcollector is highly resistance to breakdown. In particular, in a longcycle of overdischarge in a high temperature environment (40° C. orhigher), rapid deterioration due to dissolution or corrosion of thecurrent collector can be prevented, and resistance of the negativeelectrode is suppressed from increasing. Moreover, by suppressing aresistance increase of the negative electrode, Joule heat is lowered,and heat generation in the negative electrode can be suppressed.

By using the current collector made of aluminum foil or aluminum alloyfoil having an average diameter of crystal grains of 50 μm or less, itis also effective to suppress deterioration due to dissolution orcorrosion of the current collector by invasion of water in a long cyclein a high temperature and high humidity environment (40° C. or higher,and 80% or higher of humidity).

Further, an increase in the strength of the current collector makes itpossible to, when manufacturing the negative electrode by suspending thenegative electrode active material, conductive agent and binder in aproper solvent, applying the suspension on the current collector, anddrying and pressing, prevent breakage of the current collector even ifthe press pressure is raised. As a result, a negative electrode of highdensity can be manufactured, and the capacity density can be enhanced.The higher density of the negative electrode makes it possible toincrease heat conductivity, and to improve the heat releasingperformance of the negative electrode. Moreover, by synergistic effectsof suppression of heat generation in the battery and enhancement of heatreleasing performance of the electrode, the elevation of batterytemperature can be suppressed.

The thickness of the current collector is preferably 20 μm or less.

The active material in the negative electrode layer intercalates lithiumions at a potential of 0.4 V or more with respect to an electrodepotential of lithium. That is, an open circuit potential forintercalating lithium ions of the active material is 0.4 V with respectto an open circuit potential of lithium metal. By using such an activematerial, pulverization due to on alloying reaction of aluminum (oraluminum alloy) and lithium can be suppressed even if members around thenegative electrode, such as the current collector, lead, and terminal,are formed of aluminum (or aluminum alloy). In other words, as thematerial of the members around the negative electrode, aluminum (oraluminum alloy) can be used instead of copper used in the prior art. Asa result, the battery voltage can be further elevated. In particular,the open circuit potential for intercalating lithium ions of the activematerial is preferably 0.4 to 3 V, more preferably 0.4 to 2 V withrespect to the open circuit potential of lithium metal.

Examples of the active material include a metal oxide, metal sulfide,metal nitride, and metal alloy capable of intercalating lithium ions atthe specified potential. Specific examples of the metal oxide includetungsten oxide (WO₃), amorphous tin oxide such asSnB_(0.4)P_(0.6)O_(3.1), tin silicon oxide (SnSiO₃), and silicon oxide(SiO). Specific examples of the metal sulfide include lithium sulfide(TiS₂), molybdenum sulfide (MoS₂), and iron sulfide (FeS, FeS₂,Li_(x)FeS₂). Specific examples of the metal nitride include lithiumcobalt nitride (Li_(x)Co_(y)N, 0<x<4.0, 0<y<0.5).

In particular, the active material is preferably a titanium-containingoxide such as a titanium-containing metal composite oxide or titaniumoxide.

Examples of the titanium-containing metal composite oxide includetitanium oxide not containing lithium when synthesizing the oxide,lithium titanium oxide, and lithium titanium composite oxide having partof constituent elements of the lithium titanium oxide replaced bydissimilar elements. Examples of the lithium titanium oxide includelithium titanate having a spinel structure (for example, Li_(4+x)Ti₅O₁₂,0≦x<3), and lithium titanate of ramsdellite (for example, Li_(2+y)Ti₃O₇,0≦y≦3). These examples of the lithium titanate are preferred becausethey are materials capable of intercalating lithium ions at a potentialof about 1.5 V with respect to an electrode potential of lithium, andvery stable electrochemically in the current collector made of aluminumfoil or aluminum alloy foil.

Examples of the titanium oxide include TiO₂, or a metal composite oxidecontaining Ti and at least one element selected from the groupconsisting of P, V, Sn, Cu, Ni, Co and Fe. TiO₂ is preferably an anatasetype and of low crystallinity upon a heat treatment temperature of 300to 500° C. Examples of the metal composite oxide containing Ti and atleast one element selected from the group consisting of P, V, Sn, Cu,Ni, Co and Fe include TiO₂—P₂O₅, TiO₂—V₂O₅, TiO₂—P₂O₅—SnO₂,TiO₂—P₂O₅—MeO (Me is at least one element selected from the groupconsisting of Cu, Ni, Co and Fe). The metal composite oxide is preferredto be a micro structure having both of a crystal phase and amorphousphase, or an amorphous phase alone. By such a micro structure, the cycleperformance may be enhanced remarkably. In particular, a lithiumtitanium oxide and a metal composite oxide containing Ti and at leastone element selected from the group consisting of P, V, Sn, Cu, Ni, Coand Fe are preferred.

In the active material, an average particle size of primary particles ispreferred to be 1 μm or less, more preferably 0.3 μm or less. A particlesize of an active material is measured in the following method by usinga laser diffraction type particle size distribution measuring device(SALD-300 manufactured by Shimadzu Corporation). More specifically,about 0.1 g of a sample, a surface active agent, and 1 to 2 mL ofdistilled water are added to a beaker, and agitated sufficiently, andthen, the mixture is put in an agitating water tank. A light intensitydistribution is measured 64 times at intervals of 2 seconds by the laserdiffraction type particle size distribution measuring device, and theaverage particle size of primary particles of an active material isdetermined by a method of analyzing particle size distribution data.

In the case of an active material of which the average particle size ofprimary particles is 1 μm or less, for example, an active materialsubstance is preferred to be pulverized to a powder of 1 μm or less asan active material precursor at the time of reaction and synthesis, andit is obtained by grinding the baked power by a grinder such as a ballmill or jet mill to 1 μm or less.

By using such an active material of which the average particle size ofprimary particles is 1 μm or less, the cycle performance can beenhanced. In particular, this effect is outstanding in quick chargingand high output discharging, and thus, it is ideal as a secondarybattery having a high input and output performance for a vehicle. Thisis because, as the particle size becomes smaller in an active materialfor intercalating and deintercalating lithium ions, the specific surfacearea of secondary particles gathering primary particles is increased,and the diffusion distance of lithium ions becomes shorter in the activematerial, so that lithium ions can intercalate and deintercalatequickly.

In the manufacture of a negative electrode including the press processmentioned above, the load on the current collector increases as theaverage particle size of primary particles of the active materialbecomes smaller. Accordingly, when aluminum foil or aluminum alloy foilis used as the current collector, the current collector may be brokendown in the press process, and the negative electrode performance islowered. On the other hand, when the current collector is made fromaluminum foil or aluminum alloy foil having an average diameter ofcrystal grains of 50 μm or less mentioned above, the strength of thecurrent collector is enhanced. Consequently, even if the negativeelectrode is manufactured by using the active material having an averagediameter of primary particles of 1 μm or less, breakdown of the currentcollector in the press process is avoided to make it possible to enhancethe reliability, and to enhance the cycle characteristics in quickcharging and high output discharging.

The conductive agent is, for example, a carbon material. Examples of thecarbon material include acetylene black, carbon black, coke, carbonfiber, and graphite.

Examples of the binder include polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVdF), fluororubber, and styrene butadienerubber.

A blending ratio of the active material, conductive agent, and binder inthe negative electrode is preferably in a range of 80 to 95 wt. % of theactive material, 3 to 20 wt. % of the conductive agent, and 2 to 7 wt. %of the binder.

A lead connected electrically to the current collector of the negativeelectrode is made of aluminum with a purity of 99 wt. % or more, oraluminum alloy with an aluminum purity of 99 wt. % or more. Inparticular, aluminum is preferred to be 99.9 wt. % or more in purity.The aluminum alloy preferably contains, for example, Mg, Fe and Si in atotal of 0.7 wt. % or less with the balance substantially of aluminum.The lead is preferably a flexible foil or plate of 100 to 500 μm inthickness and 2 to 20 mm in width. Lead is not dissolved in anelectrolyte solution in an overdischarged state, and is not broken evenby vibration for a long period to allow a large current to flow.Consequently, long-term reliability and high output of the secondarybattery can be maintained.

At least the surface of the negative electrode terminal connected to thelead is made of aluminum alloy which has a composition containing atleast one metal selected from the group consisting of Mg, Cr, Mn, Cu,Si, Fe and Ni, having an aluminum purity of less than 99 wt. %,preferably aluminum purity of 90 wt. % or more and less than 99 wt. %.Such an aluminum alloy is higher in strength and corrosion resistance ascompared with an aluminum of a purity of more than 99 wt. % or aluminumalloy of an aluminum purity of more than 99 wt. %. Of the metal, Mg andCr contribute to enhancement of corrosion resistance of aluminum alloy,and Mn, Cu, Si, Fe and Ni contribute to enhancement of strength ofaluminum alloy.

Specific configurations of the negative electrode terminal include thefollowing.

(1) A negative electrode terminal is composed of a terminal body made ofat least one metal selected from the group consisting of copper, ironand nickel, and a layer of aluminum alloy of the above-describedcomposition, the layer being formed on the surface of the terminal bodyto which at least the lead is connected, for example, on the entiresurface of the terminal body. Since this negative electrode terminal hasa terminal body of iron, it is stronger than the aluminum alloy layer,thus the strength can be increased.

(2) A negative electrode terminal has a single structure composed ofaluminum alloy of the above-described composition.

The aluminum alloy layer of (1) above is preferred to have a thicknessof 10 to 300 If the thickness of the aluminum alloy layer is less than10 μm, connection reliability with the negative electrode lead may belowered. If the thickness of the aluminum alloy layer is exceeds 300 μm,on the other hand, smoothness and uniformity of the aluminum alloy layermay be lowered. Examples of a method of forming the aluminum alloy layerincludes a method of immersing the terminal body in a fused matter ofaluminum alloy, a method of spraying aluminum alloy onto the terminalbody, and a method of plating aluminum alloy only on the entireterminal. When forming an aluminum alloy layer only on the leadconnection surface of the terminal body by these methods, a method ofmasking a region of the terminal body excluding the lead connectionsurface may be employed.

The aluminum alloy layer is preferred to have a composition containingat least one metal selected from the group consisting of 0.5 to 5 wt. %of Mg, 0.5 wt. % or less of Cr, 0.3 to 2.0 wt. % of Mn, 5 wt. % or lessof Cu, 1 wt. % or less of Si, 1 wt. % or less of Fe, and 1 wt. % or lessof Ni, with the balance substantially composed of Al. In particular,when it is desired to realize an aluminum alloy layer excellent incorrosion resistance, it is preferred to form it with a composition ofAl—Mg alloy (Mg: 0.5 to 5 wt. %). If an aluminum alloy layer of highercorrosion resistance or strength is desired, it is preferred to contain,in addition to Mg, at least one metal selected from Mn, Cu, Si, Fe andNi in the composition by the above-described amount. Such an aluminumalloy layer is most preferred to have a composition containing 0.5 to 5wt. % of Mg, 0.3 to 2.0 wt. % of Mn, and 0.1 wt. % or less of at leastone metal selected from Cu, Fe, Si and Cr, with the balancesubstantially composed of Al. A negative electrode terminal having suchan aluminum alloy layer higher in corrosion resistance and strength canreduce the resistance at a connecting portion with the lead in a hightemperature and high humidity environment, and even when assembled in abattery module, the connection resistance among adjacent batteries canbe maintained at a low level.

When the aluminum alloy layer is formed by plating, it is preferred, dueto restrictions of plating components, to compose it by using at leastone metal selected from the group consisting of Cu, Fe, Si and Cr by 1.0wt. % or less, the balance being Al.

The negative electrode terminal of a single structure composed ofaluminum alloy of (2) above preferably has a composition comprising atleast one metal selected from the group consisting of 0.5 to 5 wt. % ofMg, 0.5 wt. % or less of Cr, 0.3 to 2.0 wt. % of Mn, 5 wt. % or less ofCu, 1 wt. % or less of Si, 1 wt. % or less of Fe, and 1 wt. % or less ofNi, substantially with the balance of Al. In particular, from theviewpoint of enhancing the strength in addition to corrosion resistance,the negative electrode terminal is preferred to be composed of analuminum alloy with a composition of Al with Mg (Mg: 0.5 to 5 wt. %) andthe above-described amount of at least one metal selected from the groupconsisting of Mn, Cu, Si, Fe and Ni. The negative electrode terminal ofthis system is most preferred to be composed of aluminum alloycontaining 0.5 to 5 wt. % of Mg, 0.3 to 2.0 wt. % of Mn, and 0.1 wt. %or less of at least one metal selected from the group consisting of Cu,Fe, Si and Cr, substantially with the balance of Al. The negativeelectrode terminal composed of such aluminum alloy enhanced in corrosionresistance and strength maintains a sufficient strength in a hightemperature and high humidity environment, and can lower the resistanceat a connection area with the negative electrode lead. In addition, evenif such a terminal is assembled in a battery module, connectionresistance among adjacent batteries can be maintained in a low state.

The shape of the negative electrode terminal is preferred to be a boltof 3 to 30 mm in diameter.

2) Positive Electrode

The positive electrode includes a current collector, and a positiveelectrode layer held on one side or both sides of the current collectorand having an active material, a conductive agent, and a binder.

The current collector is desired to be made of aluminum foil or aluminumalloy foil, with the average diameter of crystal grains of 50 μm orless, preferably 10 μm or less, as in the current collector of thenegative electrode mentioned above. Such an aluminum foil or aluminumalloy foil having the average diameter of crystal grains of 50 μm orless can increase the strength dramatically. For this reason, when apositive electrode is fabricated by suspending the active material,conductive agent and binder in a proper solvent, applying the suspensionon the current collector, and drying and pressing, breakage of thecurrent collector can be prevented even if the press pressure is raised.As a result, a positive electrode of high density can be obtained, andthe capacity density can be enhanced.

A thickness of the current collector is preferably 20 μm or less.

Examples of the active material in the positive electrode layer includean oxide, sulfide and polymer.

Examples of the oxide include manganese dioxide (MnO₂), iron oxide,copper oxide, nickel oxide, lithium manganese composite oxide (forexample, Li_(x)Mn₂O₄ or Li_(x)MnO₂), lithium nickel composite oxide (forexample, Li_(x)NiO₂), lithium cobalt composite oxide (LiCoO₂), lithiumnickel cobalt composite oxide (for example, Li_(x)Ni_(1-y)Co_(y)O₂),lithium nickel manganese cobalt composite oxide (for example,Li_(x)Co_(1-y-z)Mn_(y)Ni_(z)O₂), spinel type lithium manganese nickelcomposite oxide (Li_(x)Mn_(2-y)Ni_(y)O₄), lithium phosphorus oxidehaving an olivin structure (for example, Li_(x)FePO₄,Li_(z)Fe_(1-y)Mn_(y)PO₄, Li_(x)CoPO₄), iron sulfate (Fe₂(SO₄)₃), andvanadium oxide (for example, V₂O₅). Unless otherwise specified, x, y andz are preferably in a range of 0 to 1. The lithium nickel cobaltmanganese composite oxide is particularly preferred to be composed ofLi_(a)Ni_(b)Co_(c)Mn_(d)O₂ (where molar ratios a, b, c and d are in arange of 0≦a<1.1, 0.1≦b≦0.5, 0≦c≦0.9, and 0.1≦d≦0.5).

Examples of the polymer include a conductive polymer material such aspolyaniline and polypyrrole, and a disulfide polymer material. Inaddition, sulfur (S), carbon fluoride or the like may be used.

Preferable examples of the active material include lithium manganesecomposite oxide, lithium nickel composite oxide, lithium cobaltcomposite oxide, lithium nickel cobalt composite oxide, spinel typelithium manganese nickel composite oxide, lithium manganese cobaltcomposite oxide, iron lithium phosphate each high in battery voltage,and lithium nickel cobalt manganese composite oxide having a laminarcrystal structure.

Examples of the conductive agent include acetylene black, carbon black,and graphite.

Examples of the binder include polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVdF), and fluororubber.

A blending ratio of the active material, conductive agent, and binder inthe positive electrode layer is preferably in a range of 80 to 95 wt. %of the active material, 3 to 20 wt. % of the conductive agent, and 2 to7 wt. % of the binder.

3) Separator

Examples of the separator include a synthetic resin unwoven fabric, apolyethylene porous film, a polypropylene porous film, and an aramidporous film.

4) Outer Container

The outer container is composed of a cylindrical metal can with abottom, and a metal lid bonded and fixed to an opening of the metal canby, for example, welding. Preferably, the metal can and lid are composedof aluminum or aluminum alloy due to the purpose of reduction of weightand resistance of corrosion. An average diameter of crystal grains ofthe aluminum or aluminum alloy is preferably 50 μm or less, morepreferably 10 μm or less. The metal can composed of such aluminum oraluminum alloy having the average diameter of crystal grains of 50 μm orless can increase the strength dramatically, and thus, the thickness canbe reduced. As a result, the heat release performance is improved, whichsuppresses elevation of battery temperature. Since the thickness of themetal can is reduced, and the deposit of an electrode group including acontained positive electrode, separator and negative electrode iseffectively increased, the energy density is increased. Accordingly, thebattery is reduced in weight and size. These features are particularlypreferred for batteries used under demanding high temperature and highenergy density etc. conditions, such as an on-board secondary battery.

The aluminum alloy for use in the outer container is preferred tocontain at least one metal selected from the group consisting of Mg, Mnand Fe. The metal can of the outer container composed of such aluminumalloy is further enhanced in strength, and the wall thickness can bereduced to 0.3 mm or less.

In the square nonaqueous electrolyte secondary battery according to thefirst embodiment, terminals of the negative electrode and positiveelectrode are mounted, for example, on the lid of the outer container soas to be insulated electrically. However, the negative electrodeterminal can be electrically connected to the outer container.

5) Nonaqueous Electrolyte

Examples of the nonaqueous electrolyte include a liquid nonaqueouselectrolyte prepared by dissolving an electrolyte in an organic solvent,a gel nonaqueous electrolyte obtained by compounding the liquidelectrolyte and a polymer material, and a solid nonaqueous electrolyteobtained by compounding a lithium salt electrolyte and a polymermaterial. As the nonaqueous electrolyte, an ionic liquid containinglithium ions may be used.

The liquid nonaqueous electrolyte is prepared by dissolving anelectrolyte in an organic solvent at concentration of 0.5 to 3 mol/L.

Examples of the electrolyte include at least one selected from the groupconsisting of LiBF₄, LiPF₆, LiAsF₆, LiClO₄, LiCF₃SO₃, LiN(CF₃SO₂)₂,LiN(C₂F₅SO₂)₃C, and LiB[(OCO)₂]₂. Among these electrolytes, LiBF₄ ishigh in corrosiveness, but is preferred because it is excellent inthermal and electrochemical stability, and is less degradable.Furthermore, it is desirable to use an electrolyte which iselectrochemically stable under a high potential. Such the electrolyte isat least one selected from the group consisting of LiPF₆ and LiBF₄.

Examples of the organic solvent include cyclic carbonate such aspropylene carbonate (PC) and ethylene carbonate (EC); chain carbonatesuch as diethylel carbonate (DEC), dimethyl carbonate (DMC), and methylethyl carbonate (MEC); chain ether such as dimethoxy ethane (DME) anddiethoxy ethane (DEE); cyclic ether such as tetrahydrofuran (THF) anddioxolane (DOX); γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane(SL). These organic solvents may be used either alone or in a mixture.It is desirable to use at least one of organic solvent selected from thegroup consisting of propylene carbonate, ethylene carbonate andγ-butyrolactone, because it has a high boiling point and a high ignitionpoint, and is excellent in thermal stability. It is more desirable touse γ-butyrolactone as an organic solvent.

It is desirable to use a nonaqueous electrolyte containing at least oneof organic solvent selected from the group consisting of propylenecarbonate, ethylene carbonate and γ-butyrolactone, and an electrolyteselected from the group consisting of LiPF₆ and LiBF₄, because it has ahigh boiling point and a high ignition point, and is excellent inthermal and electrochemical stability.

Examples of the polymer material include polyvinylidene fluoride (PVdF),polyacrylonitrile (PAN), and polyethylene oxide (PEO).

The ionic liquid is composed of a lithium ion, organic cation, andorganic anion, and it is in a liquid form at 100° C. or less, or at roomtemperature or less depending on the condition.

Now, the square nonaqueous electrolyte secondary battery according tothe first embodiment will be specifically explained with reference toFIGS. 1 to 3.

A square nonaqueous electrolyte secondary battery 20 comprises an outercontainer 1 formed of, for example, aluminum alloy. The outer container1 includes a rectangular cylindrical metal can 2 with a bottom, and asquare flat lid 3 bonded airtightly to an upper end opening of the metalcan 2 by, for example, laser welding. The lid 3 has holes 4, 5 forholding a negative electrode terminal and a positive electrode terminalwhich will be described later.

A laminated electrode group 6 is contained in the metal can 2 of theouter container 1. The laminated electrode group 6 has a structure inwhich plural negative electrodes 8 and positive electrodes 9 areinserted and laminated alternately in folded parts of a separator 7folded like a hairpin as shown in FIG. 3, and the ends of the separator7 are wound so as to cover the outer side of a rectangular columnarlaminated body. Such a laminated electrode group 6 is inserted andcontained in the metal can 2 such that the hairpin folded sides of theseparator 7 may be at the upper and lower ends. An insulating plate 10is arranged between the inside of the bottom of the metal can 2 and thelower end face of the laminated electrode group 6. A nonaqueouselectrolyte is contained in the metal can 2 in which the laminatedelectrode group 6 is located.

A tubular insulating member 11 having circular flanges at both endsthereof is fitted into the hole 4 of the lid 3. For example, abolt-shaped negative electrode terminal 12 is inserted in the tubularinsulating member 11 with its head positioned in the metal can 2, andits threaded portion projects outside from the lid 3. A nut 13 made of,for example, aluminum alloy is screwed into the projecting threadedportion of the negative electrode terminal 12 by way of a washer (notshown) made of aluminum alloy, and the negative electrode terminal 12 isinsulatedly fixed to the lid 3. The negative electrode terminal 12 isformed of, for example, aluminum alloy with an aluminum purity of lessthan 99 wt. %, containing at least one metal component selected from thegroup consisting of Mg, Cr, Mn, Cu, Si, Fe and Ni.

A tubular insulating member 14 having circular flanges at both endsthereof is fitted into the hole 5 of the lid 3. For example, abolt-shaped positive electrode terminal 15 is inserted in the tubularinsulating member 14 with its head positioned in the metal can 2, andits threaded portion projects outside from the lid 3. A nut 16 made of,for example, aluminum alloy is screwed into the projecting threadedportion of the positive electrode terminal 15 by way of a washer (notshown) made of aluminum alloy, and the positive electrode terminal 15 isinsulatedly fixed to the lid 3. The positive electrode terminal 15 ismade of, for example, aluminum alloy containing a metal such as Mg, Cr,Mn, Cu, Si, Fe and Ni.

A plurality of belt-like negative electrode leads 17 composed of foilsor plates have one ends respectively connected to the negativeelectrodes 8 of the laminated electrode group 6 by, for example,resistance welding, and the other ends gathered and connected to thelower end face of the negative electrode terminal 12 by, for example,resistance welding. Like the negative electrode lead 17, a plurality ofbelt-like positive electrode leads 18 composed of foils or plates haveone ends respectively connected to the positive electrodes 9 of thelaminated electrode group 6 by, for example, resistance welding, and theother ends gathered and connected to the lower end face of the positiveelectrode terminal 15 by, for example, resistance welding. The negativeelectrode leads 17 and positive electrode leads 18 are made of aluminumwith a purity of 99 wt. % or more, or aluminum alloy with an aluminumpurity of 99 wt. % or more.

The negative electrode terminal 12 is not limited to a single structureformed of aluminum alloy of the composition shown in FIG. 1 or FIG. 2.As shown in FIG. 4, the negative electrode terminal 12 may have astructure in which the entire outer surface of a bolt-like terminal body12 a composed of at least one metal selected from the group consistingof copper, iron and nickel, is coated with a layer 12 b of aluminumalloy with aluminum purity of less than 99 wt. % containing at least onemetal selected from the group consisting of Mg, Cr, Mn, Cu, Si, Fe andNi. Or, as shown in FIG. 5, the negative electrode terminal 12 may becomposed such that the lead connection side (lower end face) of thebolt-like terminal body 12 is covered with the aluminum alloy layer 12b.

A battery module according to the first embodiment will be explainedbelow.

The battery module according to the first embodiment has a structure inwhich a plurality of the square nonaqueous electrolyte secondarybatteries are connected.

The secondary batteries can be connected by series connection, parallelconnection or series-parallel combined connection.

The battery module according to the first embodiment will bespecifically described with reference to FIG. 6. The battery module hasa structure in which a plurality of, for example, five square nonaqueouselectrolyte secondary batteries 20 shown in FIGS. 1 and 2 are arrangedin one direction, and terminals 15, 12 of the positive and negativeelectrodes of the secondary batteries are mutually connected in seriesby using connection leads 21 to 24 made of, for example, Cu. Thepositive electrode terminal 15 of the leftmost secondary battery 20 isconnected to a positive electrode pickup lead 25, and the negativeelectrode terminal 12 of the rightmost secondary battery 20 is connectedto a negative electrode pickup lead 26.

The square nonaqueous electrolyte secondary battery according to thefirst embodiment includes a negative electrode having an active materialfor intercalating lithium ions at a potential of 0.4 V or more withrespect to an electrode potential of lithium. The negative electrode hasan internal resistance of 10 mΩ or less as an alternating-currentimpedance value of 1 kHz, that is, a discharge capacity of 2 Ah or more.A lead for electrically connecting the negative electrode and thenegative electrode terminal is formed of aluminum with a purity of 99wt. % or more, or aluminum alloy with an aluminum purity of 99 wt. % ormore. Further, at least the surface of the negative electrode terminalwhich is connected to the lead is formed of aluminum alloy with analuminum purity of less than 99 wt. % containing at least one metalselected from the group consisting of Mg, Cr, Mn, Cu, Si, Fe and Ni.

Use of such a negative electrode having an active material forintercalating lithium ions at a specific potential provides thefollowing advantage. That is, even if the members around the negativeelectrode such as the current collector, lead and terminal are made ofaluminum (or aluminum alloy), it is possible to suppress pulverizationdue to an alloying reaction of the aluminum (or aluminum alloy) andlithium. More specifically, the negative electrode lead can be made ofaluminum or aluminum alloy of low resistance, and at least the leadconnecting portion of the negative electrode terminal can be made ofaluminum alloy of low resistance containing a specific metal.

At least the surface of the negative electrode terminal which isconnected to the lead is formed of aluminum alloy with an aluminumpurity of less than 99 wt. % containing at least one metal selected fromthe group consisting of Mg, Cr, Mn, Cu, Si, Fe and Ni. Consequently, thestrength and corrosion resistance of the connecting portion with thenegative electrode lead are enhanced as compared with the case offorming the surface by using aluminum with a purity of more than 99 wt.%, or aluminum alloy with a purity of more than 99 wt. %. In particular,when at least the surface of the negative electrode terminal which isconnected to the lead is formed of aluminum alloy comprising 0.5 to 5wt. % of Mg, 0.3 to 2.0 wt. % of Mn, and 0.1 wt. % of at least one metalselected from Cu, Fe, Si and Cr, with the balance substantially composedof Al, the strength and corrosion resistance of the connecting portionbetween the negative electrode terminal and the lead are furtherenhanced.

As a result, even if the secondary battery is exposed to vibration orimpact, breakage of the connecting portion between the negativeelectrode terminal and the lead can be suppressed, and a highreliability is assured.

Even if the connecting portion between the negative electrode terminaland the lead is exposed to an overdischarge operation or hightemperature and high humidity environment during a log period of use,corrosion and dissolving reaction of the connecting portion can beprevented, and a low resistance connection can be maintained. For thisreason, a high output can be obtained, and without causing elevation ofimpedance in high output discharge, a sufficient discharge reaction ofthe positive electrode and negative electrode is assured to enhance theutility rate of the active material.

Moreover, the corrosion resistance of the connecting portion between thenegative electrode terminal and the lead can be enhanced. As result, asthe electrolyte of the nonaqueous electrolyte, it is possible to useLiBF₄ which is very corrosive, but excellent in thermal and chemicalstability, and is less degradable. Consequently, high output can beobtained more stably.

Therefore, the connection reliability between the negative electrodeterminal and the lead is enhanced under the conditions of a hightemperature and high humidity environment for a long period, quickcharging, overdischarging, and high output discharge. As a consequence,it is possible to provide a square nonaqueous electrolyte secondarybattery having an excellent cycle performance and output characteristicsand high reliability.

By connecting and combining the plurality of square nonaqueouselectrolyte secondary batteries described above, favorable capacitybalance can be maintained in a individual secondary batteries under theconditions of high temperature and high humidity environment for a longperiod, quick charging, overdischarging, and high output discharge,which makes it possible to provide a battery module excellent in cycleperformance and output characteristics.

Second Embodiment

A square nonaqueous electrolyte secondary battery according to a secondembodiment comprises a metal outer container serving also as a negativeelectrode terminal, a nonaqueous electrolyte contained in the container,a positive electrode contained in the container, a negative electrodecontained in the container and having an active material forintercalating lithium ions at a potential of 0.4 V or more with respectto an electrode potential of lithium, and a separator interposed betweenthe negative electrode and the positive electrode. A negative electrodelead has one end connected to the negative electrode, and the other endconnected to the inner surface of the outer container. The negativeelectrode lead is made of aluminum with a purity of 99 wt. % or more, oraluminum alloy with an aluminum purity of 99 wt. % or more. In the outercontainer to which such a negative electrode lead is connected, at leastthe inner surface, which is connected to the negative electrodeterminal, is formed of aluminum alloy with an aluminum purity of lessthan 99 wt. % containing at least one metal selected from the groupconsisting of Mg, Cr, Mn, Cu, Si, Fe and Ni. The positive electrode isconnected to a positive electrode terminal fitted, for example, to thecontainer through a lead. Such a secondary battery has an internalresistance of about 10 mΩ or less as an alternating-current impedancevalue of 1 kHz. That is, the secondary battery has a large dischargecapacity of, for example, 2 Ah or more.

Now, the outer container will be specifically described. Note that thenegative electrode, positive electrode, separator, and nonaqueouselectrolyte are the same as those explained in the first embodiment.

The outer container includes a cylindrical metal can with a bottom, anda metal lid bonded and fixed to an opening of the metal can by, forexample, welding. More specifically, the negative electrode lead isconnected to either the inner surface of the metal can or the lidcomposing the outer container. In the outer container having such aconfiguration, at least the inner surface to which the negativeelectrode terminal is connected is made of aluminum alloy which has acomposition containing at least one metal selected from the groupconsisting of Mg, Cr, Mn, Cu, Si, Fe and Ni, having an aluminum purityof less than 99 wt. %, preferably aluminum alloy with an aluminum purityof 90 wt. % or more and less than 99 wt. %. Such an aluminum alloy canenhance the strength and corrosion resistance as compared with aluminumwith a purity of more than 99 wt. %, or aluminum alloy with a purity ofmore than 99 wt. %. Of the metals, Mg and Cr contribute to corrosionresistance of aluminum alloy, and Mn, Cu, Si, Fe and Ni contribute toenhance the strength of aluminum alloy.

Specific configurations of the outer container include the following.

(1) An outer container is made of aluminum or aluminum alloy, and has alayer of aluminum alloy of the above-described composition, the layerbeing formed on at least the inner surface to which the negativeelectrode lead is connected, for example, on the entire inner surface.In particular, when the negative electrode lead is connected to the lidof the outer container in consideration of the convenience of assemblingthe secondary battery, a structure having a layer of aluminum alloy ofthe above-described composition in the inner surface of the lid ispreferable.

(2) An outer container is composed of a metal can, and a metal lidjoined to an opening of the metal can. At least the metal can and thelid is made of aluminum alloy of the above-described composition.

The aluminum alloy layer in (1) above is preferred to have a thicknessof 10 to 300 μm. If the thickness of the aluminum alloy layer is lessthan 10 the connection reliability with the lead may be lowered. If thethickness of the aluminum alloy layer exceeds 300 μm, on the other hand,smoothness and uniformity of the aluminum alloy layer may be lowered.Examples of a method of forming the aluminum alloy layer include amethod of immersing aluminum alloy in a fused matter, a method ofspraying aluminum alloy, and a method of plating aluminum alloy. Whenthe aluminum alloy layer is formed only in the lead connection innersurface of the outer container by these methods, the area of the outercontainer excluding the lead connection surface may be protected bymasking.

The aluminum alloy layer is preferably composed of at least one metalselected from the group consisting of 0.5 to 5 wt. % of Mg, 0.5 wt. % orless of Cr, 0.3 to 2.0 wt. % of Mn, 5 wt. % or less of Cu, 1 wt. % orless of Si, 1 wt. % or less of Fe, and 1 wt. % or less of Ni, with thebalance substantially composed of Al. In particular, when it is desiredto realize an aluminum alloy layer particularly excellent in corrosionresistance, it is preferred to form it with a composition of Al—Mg alloy(Mg: 0.5 to 5 wt. %). If an aluminum alloy layer of higher corrosionresistance or strength is desired, it is preferred to contain, inaddition to Mg, at least one metal selected from the group consisting ofMn, Cu, Si, Fe and Ni in the composition by the above-described amount.Such an aluminum alloy layer is most preferred to have a composition of0.5 to 5 wt. % of Mg, 0.3 to 2.0 wt. % of Mn, and 0.1 wt. % or less ofat least one metal selected from the group consisting of Cu, Fe, Si andCr, with the balance substantially composed of Al. The outer containerhaving such an aluminum alloy layer higher in corrosion resistance andstrength can reduce the resistance at the connecting portion with thelead in a high temperature and high humidity environment, and even whenassembled in a battery module, the connection resistance among adjacentcells can be maintained at a low level.

When the aluminum alloy layer is formed by plating, it is preferred, dueto restrictions of plating components, to compose it by using at leastone metal selected from the group consisting of Cu, Fe, Si and Cr by 1.0wt. % or less, with the balance substantially of Al.

In addition, when in the outer container composed of aluminum alloy of(2) above, both the metal can and lid as constituent members are made ofaluminum alloy of the above-described composition containing a metalsuch as Mn, the metal can and lid may be made of the same composition ordifferent compositions. The outer container preferably has a compositioncomprising at least one metal selected from the group consisting of 0.5to 5 wt. % of Mg, 0.5 wt. % or less of Cr, 0.3 to 2.0 wt. % of Mn, 5 wt.% or less of Cu, 1 wt. % or less of Si, 1 wt. % or less of Fe, and 1 wt.% or less of Ni, with the balance substantially of Al. In particular,due to purpose of enhancing the strength of the outer container inaddition to corrosion resistance, the outer container is preferred to beformed of aluminum alloy in a composition of Al with Mg (Mg: 0.5 to 5wt. %) and the above-described amount of at least one metal selectedfrom Mn, Cu, Si, Fe and Ni. The outer container of this alloy system ismost preferred to be formed of aluminum alloy comprising 0.5 to 5 wt. %of Mg, 0.3 to 2.0 wt. % of Mn, and 0.1 wt. % or less of at least onemetal selected from the group consisting of Cu, Fe, Si and Cr, with thebalance substantially of Al. The outer container composed of such analuminum alloy enhanced in corrosion resistance and strength maintains asufficient strength in a high temperature and high humidity environment,and can lower the resistance at the connecting portion with the negativeelectrode lead. Hence, when assembled in a battery module, theconnection resistance among adjacent cells can be maintained in a lowstate.

In the metal can composing the outer container, it is desired todetermine the composition of aluminum alloy in consideration of theprocessability of forming a can shape, in addition to corrosionresistance and strength.

A negative electrode terminal for connection with an external lead maybe directly connected electrically to the outer container. In such aconfiguration, the negative electrode terminal may be installed in anyposition of the outer container. More preferably, the negative electrodeterminal is directly connected to the lid of the outer container fromthe viewpoint of design of the secondary battery.

In the square nonaqueous electrolyte secondary battery according to thesecond embodiment, the positive electrode terminal is connected to thelid of the outer container, for example, by electrical insulation.

Now, the square nonaqueous electrolyte secondary battery according tothe second embodiment will be specifically explained with reference toFIGS. 7 and 8.

A square nonaqueous electrolyte secondary battery 50 comprises an outercontainer 31. The outer container 31 includes a rectangular cylindricalmetal can 32 with a bottom and a square flat lid 33. The metal can 32 ismade of aluminum alloy with an aluminum purity of less than 99%containing at least one metal selected from the group consisting of Mg,Cr, Mn, Cu, Si, Fe and Ni. The lid 33 is made of the same aluminum alloyand bonded airtightly to an upper end opening of the metal can 32 by,for example, laser welding. The lid 33 has a hole 34 for holding apositive electrode terminal which will be described later.

A laminated electrode group 35 is contained in the metal can 32 of theouter container 31. The laminated electrode group 35 is composed asshown in FIG. 3. That is, the laminated electrode group 35 has astructure in which a plurality of negative electrodes 37 and positiveelectrodes 38 are alternately inserted and laminated in folded parts ofa separator 36 of the laminated electrode group 35 folded like ahairpin, and the ends of the separator 36 are wound so as to cover theouter side of a rectangular columnar laminated body. Such a laminatedelectrode group 35 is inserted and contained in the metal can 32 suchthat the hairpin folded sides of the separator 36 may be at the upperand lower ends. An insulating plate 39 is arranged between the inside ofthe bottom of the metal can 32 and the lower end face of the laminatedelectrode group 35. A nonaqueous electrolyte is contained in the metalcan 32 in which the laminated electrode group 35 is located.

A plurality of belt-like negative electrode leads 40 composed of foilsor plates have one ends connected to the negative electrodes 37 of thelaminated electrode group 35 by, for example, resistance welding, andthe other ends gathered and connected to the inner surface of the lid 33of the outer container 31 by, for example, resistance welding. Thenegative electrode lead 40 is made of aluminum with a purity of 99 wt. %or more, or aluminum alloy with an aluminum purity of 99 wt. % or more.

A tubular insulating member 41 having circular flanges at both endsthereof is fitted into the hole 34 of the lid 33. For example, abolt-shaped positive electrode terminal 42 is inserted in the tubularinsulating member 41 with its head positioned in the metal can 32, andits threaded portion projects outside from the lid 33. A nut 43 made of,for example, aluminum alloy is screwed into the projecting threadedportion of the positive electrode terminal 42 by way of a washer (notshown) made of aluminum alloy, and the positive electrode terminal 42 isinsulatedly fixed to the lid 33. A plurality of belt-like positiveelectrode leads 44 composed of foils or plates have one ends connectedto the positive electrodes 38 of the laminated electrode group 35 by,for example, resistance welding, and the other ends gathered andconnected to the lower end face of the positive electrode terminal 42by, for example, resistance welding. The positive electrode lead 44 ismade of aluminum with a purity of 99 wt. % or more, or aluminum alloywith an aluminum purity of 99 wt. % or more.

A battery module according to the second embodiment will be explainedbelow.

The battery module according to the second embodiment is composed byconnecting a plurality of the square nonaqueous electrolyte secondarybatteries described above.

The secondary batteries can be connected by series connection, parallelconnection or series-parallel combined connection.

Such a battery module according to the embodiment will be specificallydescribed with reference to FIG. 9. The battery module has a structurein which a plurality of, for example, five square nonaqueous electrolytesecondary batteries 50 shown in FIGS. 6 and 7 are arranged in onedirection, and the positive electrode terminal 42 of the secondarybatter 50 and the lid 33 of the outer container 31 serving also as anegative electrode terminal are mutually connected in series by usingconnection leads 51 to 54 made of, for example, Cu. The positiveelectrode terminal 42 of the leftmost secondary battery 50 is connectedto a positive electrode pickup lead 55, and the lid 33 serving also as anegative electrode terminal of the rightmost secondary battery 50 isconnected to a negative electrode pickup lead 56.

The square nonaqueous electrolyte secondary battery according to thesecond embodiment includes a negative electrode having an activematerial for intercalating lithium ions at a potential of 0.4 V or morewith respect to an electrode potential of lithium. The negativeelectrode has an internal resistance of 10 mΩ or less as analternating-current impedance of 1 kHz, that is, a discharge capacity of2 Ah or more. A negative electrode lead for electrically connecting thenegative electrode and the outer container serving as a negativeelectrode terminal is made of aluminum with a purity of 99 wt. % ormore, or aluminum alloy with an aluminum purity of 99 wt. % or more.Further, at least the inner surface of the outer container which isconnected to the lead is formed of aluminum alloy with an aluminumpurity of less than 99 wt. % containing at least one metal selected fromthe group consisting of Mg, Cr, Mn, Cu, Si, Fe and Ni.

Use of such a negative electrode having an active material forintercalating lithium ions at a specific potential provides thefollowing advantage. That is, even if the members around the negativeelectrode such as the current collector, lead and terminal are formed ofaluminum (or aluminum alloy), it is possible to suppress pulverizationdue to an alloying reaction of the aluminum (or aluminum alloy) andlithium. More specifically, since the negative electrode lead can beformed of aluminum or aluminum alloy of low resistance, the outercontainer can be formed of aluminum or aluminum alloy, and can beconnected to the negative electrode lead. In other words, the outercontainer serves also as a negative electrode terminal. As a result, theouter container can be formed of aluminum alloy of low resistancecontaining a specific metal, at least in the portion connecting with thelead, as in the negative electrode terminal of the first embodiment.

At least the inner surface of the outer container which is connected tothe lead is made of aluminum alloy with an aluminum purity of less than99 wt. % containing at least one metal selected from the groupconsisting of Mg, Cr, Mn, Cu, Si, Fe and Ni. Consequently, the strengthand corrosion resistance of the connecting portion with the negativeelectrode lead can be enhanced as compared with the case of forming theconnecting portion by using aluminum with a purity of more than 99 wt.%, or aluminum alloy with an aluminum purity of more than 99 wt. %. Inparticular, when at least the inner surface of the outer container whichis connected to the lead is formed of aluminum alloy comprising 0.5 to 5wt. % of Mg, 0.3 to 2.0 wt. % of Mn, and 0.1 wt. % of at least one metalselected from the group consisting of Cu, Fe, Si and Cr, with thebalance substantially composed of Al, the strength and corrosionresistance of the connecting portion between the outer container servingas a negative electrode terminal and the lead are further enhanced. Inparticular, by forming the metal can composing the outer container byusing aluminum alloy of the above-described composition, the strength ofthe metal can is enhanced. In addition, since the strength is increased,the wall thickness can be reduced.

As a result, even if the secondary battery is exposed to vibration orimpact, breakage of the connecting portion between the outer containerserving as a negative electrode terminal and the negative electrode leadcan be suppressed, and a high reliability is assured.

Even if the connecting portion between the outer container and thenegative electrode lead is exposed to an overdischarge operation or hightemperature and high humidity environment during a log period of use, acorrosion and dissolving reaction can be prevented at the connectingportion, and low resistance connection can be maintained. For thisreason, a high output can be obtained, and without causing elevation ofimpedance in high output discharge, a sufficient discharge reaction ofthe positive electrode and negative electrode is assured, and theutility rate of the active material is enhanced.

Further, corrosion resistance of the connecting portion between theouter container and the negative electrode lead can be enhanced. Asresult, as the electrolyte of the nonaqueous electrolyte, it is possibleto use LiBF₄ which is very corrosive, but excellent in thermal andchemical stability, and is less degradable. Consequently, a high outputcan be obtained more stably.

Therefore, the connection reliability between the outer containerserving as a negative electrode terminal and the lead is enhanced underthe conditions of a high temperature and high humidity environment for along period, quick charging, overdischarging, and high output discharge.This makes it possible to provide a square nonaqueous electrolytesecondary battery having an excellent cycle performance and outputcharacteristics and high reliability.

By connecting and combining a plurality of the square nonaqueouselectrolyte secondary batteries described above, a favorable capacitybalance is maintained in individual secondary batteries under theconditions of a high temperature and high humidity environment for along period, quick charging, overdischarging, and high output discharge.Accordingly, it is possible to provide a battery module excellent incycle performance and output characteristics.

Now, examples of the invention will be described. The invention is notlimited to the following examples alone, but may be changed and modifiedfreely within the scope not departing from the true spirit thereof.

Example 1 Preparation of Negative Electrode

Lithium titanate (Li₄Ti₅O₁₂) having an average diameter of primaryparticles of 0.5 and specific surface area of BET by N₂ gas of 20 m²/gas an active material, carbon powder having an average particle size of4 μm as a conductive agent, and polyvinylidene fluoride (PVdF) as abinder were blended by 90:7:3 by weight, and the mixture was dispersedin an n-methyl pyrrolidone (NMP) solvent to prepare a slurry. The slurrywas applied to an aluminum alloy foil (current collector) to a thicknessof 15 μm, with an average diameter of crystal grains of 50 μm, andpurity of 99 wt. %, and dried, pressed, and cut to prepare 60 plates ofnegative electrodes with a size of 140 mm×330 mm and electrode densityof 2.5 g/cm³. A belt-like lead made of aluminum foil with a width of 10mm, a length of 30 mm, thickness of 200 μm, and purity of 99.9 wt. % wasbonded to one end of the current collector of each of the negativeelectrodes by resistance welding.

<Preparation of Positive Electrode>

Lithium cobalt oxide (LiCoO₂) as an active material, graphite powder asa conductive agent, and polyvinylidene fluoride (PVdF) as a binder wereblended by 87:8:5 by weight, and the mixture was dispersed in a n-methylpyrrolidone (NMP) solvent to prepare a slurry. The slurry was applied toan aluminum alloy foil (current collector) to a thickness of 15 μm, withan average diameter of crystal grains of 10 μm, and purity of 99 wt. %,and dried, pressed, and cut to prepare 61 plates of positive electrodeswith a size of 140 mm×330 mm and electrode density of 3.5 g/cm³. Abelt-like lead made of aluminum foil with a width of 10 mm, a length of30 mm, thickness of 200 μm, and purity of 99.9 wt. % was bonded to oneend of the current collector of each of the positive electrodes byresistance welding.

<Preparation of Lid with Terminal>

In a lid made of aluminum alloy with a length of about 141.6 mm, a widthof about 14.6 mm, thickness of 0.3 mm, comprising 1.6 wt. % of Mg, 1 wt.% of Mn, 0.4 wt. % of Fe, and the balance substantially of Al, holes forholding a negative electrode terminal and a positive electrode terminalwere opened. A tubular insulating member having circular flanges at bothends thereof was fitted in each hole of the lid. A bolt-like negativeelectrode terminal with a head diameter of 10 mm was inserted in thetubular insulating member of the lid, and its threaded portion wasprotruded to the lid side opposite to the head. A bolt made of aluminumalloy was screwed in to the threaded portion through a washer made ofaluminum alloy, so that the negative electrode terminal was fixed to thelid through one tubular insulating member. The negative electrodeterminal was formed of aluminum alloy comprising 1 wt. % of Mg, 0.6 wt.% of Si, 0.25 wt. % of Cu, and the balance substantially of Al.Subsequently, a bolt-like positive electrode terminal with a headdiameter of 10 mm was inserted in the other tubular insulating member ofthe lid, and its threaded portion was protruded to the lid side oppositeto the head. A bolt made of aluminum alloy was screwed in this threadedportion through a washer made of aluminum alloy, so that the positiveelectrode terminal was fixed to the lid through the tubular insulatingmember. The positive electrode terminal was formed of aluminum alloycomprising 1 wt. % of Mg, 0.6 wt. % of Si, 0.25 wt. % of Cu, and thebalance substantially of Al.

The bolt and washer were formed of aluminum alloy comprising 1 wt. % ofMg, 0.6 wt. % of Si, 0.25 wt. % of Cu, and the balance substantially ofAl.

<Assembling of Secondary Battery>

In folded portions of a separator composed of a polyethylene porous filmof 12 μm in thickness folded like a hairpin, the 60 negative electrodesbonded with negative electrode leads and the 61 positive electrodesbonded with positive electrode leads were alternately inserted andlaminated, and ends of the separator were wound so as to cover the outerside of a rectangular columnar laminated body to prepare an electrodegroup 2 as shown in FIG. 3. The laminated electrode group was furtherpressed and molded, and then inserted into a rectangular tubular metalcan with the bottom. The metal can was formed of aluminum alloycomprising 1.6 wt. % of Mg, 1 wt. % of Mn, 0.4 wt. % of Fe, and thebalance substantially of Al, and was cut in a size of 335 mm in height,142 mm in length, 15 mm in width, and 0.2 mm in thickness. Then, as anonaqueous electrolyte, an electrolyte obtained by dissolving lithiumsalt LiBF₄ in a mixed solvent of organic solvents EC and GBL (1:2 byvolume) by 1.5 mol/L was poured in the metal can. Subsequently, the lidwas placed such that the heads of terminals of the negative electrodeand positive electrode were positioned at the opening side of the metalcan. The leading ends of the negative electrode leads connected to thenegative electrodes of the laminated electrode group in the metal canwere gathered at the lower side of the head of the negative electrodeterminal and bonded by resistance welding, and the leading ends of thepositive electrode leads connected to the positive electrodes of thelaminated electrode group were gathered at the lower side of the head ofthe positive electrode terminal and bonded by resistance welding.Thereafter, the lid was fitted to the opening of the metal can, and theouter edge of the lid and the opening of the metal can were connected bylaser welding to compose an outer container. Consequently, a squarenonaqueous electrolyte secondary battery with a height of 335 mm, lengthof 142 mm, width of 15 mm, and discharge capacity of 40 Ah as shown inFIGS. 1 and 2 was manufactured. A resistance value ofalternating-current impedance of 1 kHz of the secondary battery was 0.5mΩ.

Examples 2 to 7

Square nonaqueous electrolyte secondary batteries were manufactured inthe same manner as in Example 1, except that a negative electrodeterminal formed of aluminum alloy having a composition shown in Table 1and a negative electrode lead formed of aluminum alloy having acomposition shown in Table 1 were used.

Example 8

A square nonaqueous electrolyte secondary battery was manufactured inthe same manner as in Example 1, except that a negative electrodeterminal was used, the negative electrode terminal being obtained bycovering the entire surface of a copper terminal body shown in FIG. 4with an aluminum alloy plating layer of 100 μm in thickness having acomposition shown in Table 1.

Example 9

A square nonaqueous electrolyte secondary battery was manufactured inthe same manner as in Example 1, except that a negative electrodeterminal was used, the negative electrode terminal being obtained bycovering the entire surface of an iron terminal body shown in FIG. 4with an aluminum alloy plating layer of 100 in thickness having acomposition Table 1.

Example 10

A square nonaqueous electrolyte secondary battery was manufactured inthe same manner as in Example 1, except that a negative electrodeterminal was used, the negative electrode terminal being obtained bycovering the entire surface of a nickel terminal body shown in FIG. 4with an aluminum alloy plating layer of 100 μm in thickness having acomposition shown in Table 1.

Example 11

A square nonaqueous electrolyte secondary battery was manufactured inthe same manner as in Example 1, except that an anatase type TiO₂ heattreated at 350° C. was used as a negative electrode active material.

Example 12

A battery module shown in FIG. 6 was assembled by connecting five squarenonaqueous electrolyte secondary batteries as in Example 1 in series byuse of copper connection leads.

Comparative Examples 1 to 5

Square nonaqueous electrolyte secondary batteries were manufactured inthe same manner as in Example 1, except that a negative electrodeterminal formed of metal shown in Table 1 was used. In Comparativeexamples 1, 4, and 5, negative electrode leads made of aluminum alloyhaving a composition shown in Table 1 were used.

Comparative Example 6

A battery module was assembled by connecting five square nonaqueouselectrolyte secondary batteries as in Comparative example 1 in series byuse of copper connection leads.

In the obtained square nonaqueous electrolyte secondary batteries inExamples 1 to 11 and Comparative examples 1 to 5, and the batterymodules in Example 12 and Comparative example 6, long-term charge anddischarge cycle tests were conducted to evaluate the output performanceafter specified cycles.

The square nonaqueous electrolyte secondary batteries were evaluatedafter 1000 cycles of a quick charge and overdischarge cycle test underhigh temperature and high humidity, and then, the output density (kW/kg)obtained from the maximum current obtained until 1.5 V in 10 seconds wasmeasured. In the quick charge and overdischarge cycle test, charging ata constant voltage (maximum current 400 A) of 2.8 V was performed for 6minutes under the environment of a temperature of 60° C. and humidity of90%, and subsequently, a constant current discharge at 400 A until 0 Vwas repeated.

The battery modules were evaluated after 1000 cycles of a quick chargeand overdischarge cycle test under high temperature and high humidity,and then, the output density (kW/kg) obtained from the maximum currentpicked up until 7.5 V in 10 seconds was measured. In the quick chargeand overdischarge cycle test, charging at a constant voltage (maximumcurrent 400 A) of 14 V was performed for 6 minutes under the environmentof a temperature of 60° C. and humidity of 90%, and subsequently, aconstant current discharge at 400 A until 7.5 V was repeated.

These results are shown in Table 1.

TABLE 1 Output density Negative electrode terminal: numerals in Negativeelectrode lead: numerals in (after 1000 cycles) parentheses denote wt. %parentheses denote wt. % (kW/kg) Example 1 Mg(1)Si(0.6)Cu(0.25)Al(balance) alloy Al(99.9) 2.0 Example 2 Mg(1.6)Mn(1)Fe(0.5)Cu(0.2)Al(balance)alloy Al(99.3) 2.3 Example 3 Mg(5)Mn(0.1)Cr(0.1)Al(balance)alloy Mg(0.5) Al(balance)alloy 1.8 Example 4Mg(0.7)Si(1)Cr(0.25) Al(balance)alloy Mg(0.5) Al(balance)alloy 1.9Example 5 Mg(0.7)Si(0.4) Al(balance)alloy Mg(0.5) Al(balance)alloy 2.0Example 6 Mg(1.4) Al(balance)alloy Mg(0.5) Al(balance)alloy 2.1 Example7 Mg(1.6)Mn(1)Fe(0.5)Cu(0.2) Al(balance)alloy Mg(0.5) Al(balance)alloy2.4 Example 8 Cu main body + Cu(0.1) Mg(1)Al(balance)plated layerAl(99.9) 2.2 Example 9 Fe main body + Fe(1.1) Al(balance)plated layerAl(99.9) 1.8 Example 10 Ni main body + Ni(0.1) Mg(1)Al(balance)platedlayer Al(99.9) 2.0 Example 11 Mg(1)Si(0.6)Cu(0.25) Al(balance)alloyAl(99.9) 2.0 Example 12 Mg(1)Si(0.6)Cu(0.25) Al(balance)alloy Al(99.9)1.6 Comparative Cu Cu(4.5) Al(balance)alloy 0.2 example 1 Comparative NiAl(99.9) 0.3 example 2 Comparative Fe Al(99.9) 0.1 example 3 ComparativeAl(99.9) Cu(4.5) Al(balance)alloy 0.5 example 4 Comparative Cu Cu(4.5)Al(balance)alloy 0.1 example 5 Comparative Cu Cu(4.5) Al(balance)alloy0.15 example 6

As is clear from Table 1, the square nonaqueous electrolyte secondarybatteries in Examples 1 to 11, each having a negative electrode leadmade of aluminum with a purity of 99 wt. % or more, or aluminum alloywith an aluminum purity of 99 wt. % or more, and a negative electrodeterminal at least the surface of which connected to the negativeelectrode lead was made of aluminum alloy with an aluminum purity ofless than 99 wt. % containing at least a metal component selected fromthe group consisting of Mg, Cr, Mn, Cu, Si, Fe and Ni, are known to besuperior in output performance after quick charge and overdischargecycles at a high temperature of 60° C. and high humidity of 90%, ascompared with Comparative examples 1 to 5.

The battery module in Example 12 manufactured by connecting five squarenonaqueous electrolyte secondary batteries in Example 1 in series isknown to be superior in output performance after quick charge andoverdischarge cycles at a high temperature of 60° C. and high humidityof 90%, as compared with the battery module in Comparative example 6manufactured by connecting five square nonaqueous electrolyte secondarybatteries in Comparative example 1 in series.

Example 13

In Example 13, a square nonaqueous electrolyte secondary battery has astructure including an outer container serving also as a negativeelectrode terminal.

<Preparation of Lid with Positive Electrode Terminal>

A hole for holding a terminal was opened in a lid composing an outercontainer serving also as a negative electrode terminal together with ametal can described below. The lid was formed of aluminum alloy with alength of about 141.6 mm, a width of about 14.6 mm, and thickness of 0.3mm, comprising 0.3 wt. % of Mg, 1.2 wt. % of Mn, 0.4 wt. % of Fe, andthe balance substantially of Al. A tubular insulating member havingcircular flanges at both ends thereof was fitted in the hole of the lid.A bolt-like positive electrode terminal with a head diameter of 10 mmwas inserted in the tubular insulating member of the lid, and itsthreaded portion was protruded to the lid side opposite to the head. Abolt made of aluminum alloy was screwed in this threaded portion througha washer made of aluminum alloy, so that the positive electrode terminalwas fixed to the lid through the tubular insulating member. The positiveelectrode terminal was formed of aluminum alloy comprising 1 wt. % ofMg, 0.6 wt. % of Si, 0.25 wt. % of Cu, and the balance substantially ofAl.

The bolt and washer were formed of aluminum alloy comprising 1 wt. % ofMg, 0.6 wt. % of Si, 0.25 wt. % of Cu, and the balance substantially ofAl.

<Assembly of Secondary Battery>

As in Example 1, a laminated electrode group was manufactured, thelaminated electrode group was inserted into a rectangular tubular metalcan with a bottom, and an electrolyte was injected into the metal can.The metal can was formed of aluminum alloy comprising 1.2 wt. % of Mn,0.1 wt. % of Si, 0.4 wt. % of Fe, and the balance substantially of Al,and was cut in a size of 335 mm in height, 142 mm in length, 15 mm inwidth, and 0.2 mm in thickness. Subsequently, the lid was placed suchthat the head of the positive terminal was positioned at the openingside of the metal can. The leading ends of the negative electrode leadsconnected to the negative electrodes of the laminated electrode group inthe metal can were gathered at the lower side of the lid and bonded byresistance welding, and the leading ends of the positive electrode leadsconnected to the positive electrodes of the laminated electrode groupwere gathered at the lower side of the head of the positive electrodeterminal and bonded by resistance welding. Thereafter, the lid wasbonded to the opening of the metal can, and the outer edge of the lidand the opening of the metal can were connected by laser welding tocompose an outer container serving also as a negative electrodeterminal. Consequently, a square nonaqueous electrolyte secondarybattery with a height of 335 mm, length of 142 mm, width of 15 mm, anddischarge capacity of 40 Ah as shown in FIGS. 7 and 8 was manufactured.A resistance value of an alternating-current impedance of 1 kHz of thesecondary battery was 0.5 mΩ.

Examples 14 and 15

Square nonaqueous electrolyte secondary batteries were manufactured inthe same manner as in Example 13, except that an outer container (metalcan and lid) made of aluminum alloy having a composition shown in Table2 and a negative electrode lead made of aluminum alloy having acomposition shown in Table 2 were used.

Example 16

A battery module shown in FIG. 9 was assembled by connecting five squarenonaqueous electrolyte secondary batteries as in Example 13 in series byuse of copper connection leads.

In the obtained square nonaqueous electrolyte secondary batteries inExamples 13 to 15, and the battery module in Example 16, long-termcharge and discharge cycle tests were conducted in the same manner as inExample 1 to evaluate the output performance after specified cycles.

These results are shown in Table 2.

TABLE 2 Outer Container Negative electrode Output density Metal can:numerals in Lid: numerals in lead: numerals in (after 1000 cycles)parentheses denote wt. % parentheses denote wt. % parentheses denote wt.% (kW/kg) Example 13 Mn(1.2)Si(0.2)Fe(0.4) Mg(0.3)Mn(1.2)Fe(0.4)Al(99.9) 1.8 Al(balance)alloy Al(balance)alloy Example 14Mn(1.0)Si(0.6)Fe(0.4) Mg(0.3)Mn(1.2)Fe(0.4) Al(99.9) 2.0Al(balance)alloy Al(balance)alloy Example 15 Mn(1.5)Si(0.1)Fe(0.4)Mg(0.2)Mn(1.2)Fe(0.4) Mg(0.5) 2.2 Al(balance)alloy Al(balance)alloyAl(balance)alloy Example 16 Mn(1.2)Si(0.1)Fe(0.4) Mg(0.1)Mn(1.2)Fe(0.4)Al(99.9) 2.0 Al(balance)alloy Al(balance)alloy

As is clear from Table 2, the square nonaqueous electrolyte secondarybatteries in Examples 13 to 15, each having a negative electrode leadmade of aluminum with a purity of 99 wt. % or more, or aluminum alloywith an aluminum purity of 99 wt. % or more, and an outer container(lid) at least the inner surface of which connected to the negativeelectrode lead was formed of aluminum alloy with a purity of less than99 wt. % containing at least a metal component selected from the groupconsisting of Mg, Cr, Mn, Cu, Si, Fe and Ni, are known to be superior inoutput performance after quick charge and overdischarge cycles at hightemperature of 60° C. and high humidity of 90%, as compared withComparative examples 1 to 5 shown in Table 1.

The battery module in Example 16 assembled by connecting five squarenonaqueous electrolyte secondary batteries in Example 13 in series isknown to be superior in output performance after quick charge andoverdischarge cycles at a high temperature of 60° C. and high humidityof 90%, as compared with the battery module in Comparative example 6shown in Table 1.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A nonaqueous electrolyte secondary battery having an internalresistance of 10 mΩ or less at an alternating-current impedance value of1 kHz, comprising: an outer container; a nonaqueous electrolyte housedin the container; a positive electrode housed in the container; anegative electrode housed in the container and comprising an activematerial for intercalating lithium ions at a potential of 0.4 V or morewith respect to an electrode potential of lithium; a separatorinterposed between the negative electrode and the positive electrode; anegative electrode lead having a first end connected to the negativeelectrode, the negative electrode lead being made of aluminum with apurity of 99 wt. % or more, or an aluminum alloy with an aluminum purityof 99 wt. % or more; a negative electrode terminal extending from theinside of the outer container to the outside so as to be connectedelectrically to a second end of the negative electrode lead, thenegative electrode terminal being made of an aluminum alloy which has analuminum purity of 90 wt. % or more and less than 99 wt. %, and whichcomprises 0.5 to 5 wt. % of Mg; a positive electrode lead having a firstend connected to the positive electrode; and a positive electrodeterminal extending from the inside of the outer container to the outsidein a same direction as a direction from which the negative electrodeterminal extends, so as to be connected electrically to a second end ofthe positive electrode lead.
 2. The secondary battery according to claim1, wherein the negative electrode terminal is made of an aluminum alloyconsisting of: 90 wt. % or more and less than 99 wt. % of Al; 0.5 to 5wt. % of Mg; and at least one metal selected from the group consistingof 0.5 wt. % or less of Cr, 0.3 to 2.0 wt. % of Mn, 5 wt. % or less ofCu, 1 wt. % or less of Si, 1 wt. % or less of Fe, and 1 wt. % or less ofNi.
 3. The secondary battery according to claim 1, wherein thenonaqueous electrolyte comprises at least one solvent selected from thegroup consisting of propylene carbonate, ethylene carbonate andγ-butyrolactone, and at least one electrolyte selected from the groupconsisting of LiPF₆ and LiBF₄.
 4. The secondary battery according toclaim 1, wherein the negative electrode has a current collector composedof an aluminum foil or aluminum alloy foil with a purity of 99 wt. % ormore.
 5. (canceled)
 6. A battery module assembled by connecting aplurality of nonaqueous electrolyte secondary batteries according toclaim
 1. 7. The secondary battery according to claim 1, wherein thenegative electrode lead is made of aluminum having a purity of 99.9 wt.% or more.
 8. The secondary battery according to claim 1, wherein thenegative electrode terminal is made of an aluminum alloy consisting of:90 wt. % or more and less than 99 wt. % of Al; 0.5 to 5 wt. % of Mg; 0.3to 2.0 wt. % of Mn; and 0.1 wt. % or less of at least one metal selectedfrom Cu, Fe, Si and Cr.
 9. The secondary battery according to claim 1,wherein the positive electrode comprises an active material selectedfrom the group consisting of lithium manganese composite oxide, lithiumnickel composite oxide, lithium cobalt composite oxide, lithium nickelcobalt composite oxide, spinel type lithium manganese nickel compositeoxide, lithium manganese cobalt composite oxide, iron lithium phosphateand lithium nickel cobalt manganese composite oxide having a laminarcrystal structure.
 10. The secondary battery according to claim 1,wherein the active material in the negative electrode is atitanium-containing oxide.
 11. The secondary battery according to claim10, wherein the titanium-containing oxide is a titanium-containing metalcomposite oxide, or titanium oxide.
 12. The secondary battery accordingto claim 10, wherein the titanium-containing metal composite oxide istitanium oxide not containing lithium when synthesizing the oxide, orlithium titanium oxide, or lithium titanium composite oxide having partof constituent elements of the lithium titanium oxide replaced bydissimilar elements.
 13. The secondary battery according to claim 12,wherein the lithium titanium composite oxide is lithium titanate havinga spinel structure, or lithium titanate of ramsdellite.
 14. Thesecondary battery according to claim 11, wherein the titanium oxide isTiO₂, or a metal composite oxide containing Ti and at least one elementselected from the group consisting of P, V, Sn, Cu, Ni, Co and Fe. 15.The secondary battery according to claim 14, wherein the metal compositeoxide is TiO₂—P₂O₅, TiO₂—V₂O₅, TiO₂—P₂O₅—SnO₂, or TiO₂—P₂O₅—MeO, whereMe is at least one element selected from the group consisting of Cu, Ni,Co and Fe.
 16. The secondary battery according to claim 6, wherein thetitanium-containing oxide is a particle having an average diameter of 1μm or less.
 17. The secondary battery according to claim 1, wherein theouter container is made of a metal.
 18. The secondary battery accordingto claim 1, wherein an electrode group is composed of the positiveelectrode, the negative electrode and the separator, and wherein pluralpositive electrode leads are extended from the positive electrodelocated in a face of the electrode group, and plural negative electrodeleads are extended from the negative electrode located in the same faceof the electrode group, from which the positive electrode leads areextended.
 19. The battery module according to claim 6, wherein thebattery module is assembled by connecting five of the secondarybatteries in series.